As Catholic health systems that restrict care on religious grounds have expanded, Maryam Guiahi had what she thought was a simple question. Guiahi, an associate professor of obstetrics and gynecology at the University of Colorado School of Medicine, wanted to know what happens to patients who are denied reproductive health care by Catholic institutions.

So she and fellow researchers trawled through thousands of papers dating back to at least the 1960s in scientific databases, looking for data on patient outcomes.

They found one study. It happened to be one Guiahi had written.

“We don’t know, when patients get denied a service, do most of them figure out a way to get it in some other way?” Guiahi told Rewire.News. “Or do most of them end up having outcomes that they were not hoping for?”

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Guiahi and her fellow researchers—who published their review in the latest issue of Obstetrics & Gynecology—found just 27 studies on reproductive health care at Catholic institutions, which now account for one in six acute-care beds in the United States. While these facilities follow religious directives that ban an array of reproductive care, most studies focused on the availability of birth control, sterilization, or emergency contraception. Two focused on abortion care. One looked at miscarriage management and one at infertility care.

Part of the reason for this lack of information is that Catholic institutions may not want it known, according to Guiahi, who has been thwarted in her research.

“At one institution, I just wanted to survey women to understand what they thought they could get at this institution—like did they think they could get a birth control pill?” Guiahi said. “And the response I got was: We prefer not to make our patients aware of what we don’t offer.”

This secrecy seems to be working. More than a third of women who rely on a Catholic hospital for reproductive services don’t realize it’s Catholic. One in five of these institutions don’t disclose their religious identity on their website, Guiahi found in another study.

Another barrier is that researchers within Catholic institutions may fear retaliation if they report on reproductive care, Guiahi said. That could explain why only two studies have been conducted by researchers within these facilities, meaning the bulk of the research comes from outsiders who don’t have access to patient information. Providers who have found ways to get around the rules and provide reproductive care at Catholic hospitals may also want to avoid publicizing the workarounds, lest the Catholic bishops find out and stop them.

But Guiahi’s lone study on patient outcomes is enough to raise concerns.

That study, from 2011, looked at what happened when the Catholic Loyola University Medical Center restricted access to injectable contraception for patients who had just given birth. Pregnancy rates over the ensuing year increased, particularly for young women of color. Overall, women of color are more likely to give birth in Catholic institutions.

Other research excluded from Guiahi’s review points to the devastating effect of reproductive health-care denial, showing, for example, that women who are denied abortions and carry unwanted pregnancies to term are more likely to suffer serious medical complications and mental health issues, or to stay with abusive partners. Their children fare worse than their peers and are more likely to live in poverty.

The lack of data on Catholic hospitals hampers meaningful public dialogue about how to regulate these hospitals, which receive billions in public funding through Medicare and Medicaid, and deprives patients of the ability to make informed choices about where to seek care. Mergers, hospital closures, and insurance policies that dictate where patients seek care have made Catholic institutions the only accessible option for many people.

There is one obvious conclusion that emerges from the research on Catholic hospitals. The availability of reproductive care in these institutions—as in secular institutions—can vary widely. A 2005 study, for example, found that 54.9 percent of Catholic hospitals do not provide emergency contraception for any reason, compared with 42.2 percent of non-Catholic hospitals. But another from 1999 found 82 percent of Catholic emergency departments do not provide emergency contraception, even for rape.

Even within the same Catholic system, religious rules around sterilization and contraception can differ.

That makes it seem a tall order for patients to understand how these directives can impact their lives, especially when not even researchers have the answer.